System for and method of producing sulphate and sulphite pulp



Dec, 16, E924.

. (su. A. RICHTER SYSTEM Foa AND METHODl oF PRODUCING SULPHATE ANDSULPHITE PULP kwh lAlII. m`\\l Patented Dec. 16, 1924.

UNITED STATES PATENT OFFICE.

GEORGE A. RICHTER, 0F BERLIN, NEW HAMPSHIREQASSIGNOR T0 BROWN COMPANY, 0F BERLIN, NEW HAMPSHIRE, A CORPORATION 0F MAINE.

SYSTEM FORAND METHOD OF PRODUCING SULPHATE AND SULPHITE PULP.

Application filed September 6, 1923. Serial No. 661,241.

To all fio/wm t may concer/nf.'

lle it known that I. GEORGE A. RICHTER, a citizen of the United States, residing at Berlin, in the county of Coos and State of New Hampshire, have invented new and useful Improvements in Systems for and Methods of Producing Sulphate and Sulphite Pulp, of which the following is a specification.

This invention relates to a process of and apparatus for nmnufacturing both sulphate and sulphite pulps from cellulosic material, of the general character of those s'et forth inmy copending application, Serial No. (358,10l, filed August 18, 1923. In said application I have pointed out that the sulphate pulp so called, is produced by cookingk the wood chips or other cellulosic material in an alkaline liquor comprising sodium sulphide and caustic soda, whereas the sulphite pulp is produced by cooking like material in an acid cooking liquor containing in addition to sulphurous acid, sodium sulphate and, preferably, sodium su-lphite, and that the soda recovered from the waste liquor resulting from one' process of digestion is employed in a suitable form in preparing the liquor for the other process of digestion, and vice versa. Likewise in said application, I have shown and described an apparatus, in which the molten soda recovered from the alkaline black liquor from the sulphate digestion, is subjected to oxidation for its recovery as sulphate and carbonate of soda, whereas that soda recovered from the waste acid liquor from the sulphite digestion is subjected to a reducing atmosphere while molten, in order that it may be recovered partly in the form of sodium sulphide. f According to the present invention, I reverse the last-mentioned operations and sub- 'cct theI molten soda from the initially alkaue waste liquor to a reducing atmosphere, and that from the initially acid liquor to an oxidizing atmosphere, and also provide certain other necessary or desirable changes which will be subsequently explained.

The accompanying drawing represents diagrammatically and conventionally a system for carrying out a process, all in accordance with the present invention. In using the term system I mean thereby to includeI vthe various mechanical instrumentalities and connections which constitute a means for carrying out my process.

Referring to the drawing, 1 indicates what may be termed for convenience the sulphate digester of the system, inasmuch as the pulp produced thereby is commercially termed sulphate pulp, although inthe digestion of the Wood no sulphate, except that which may be adventitiously present, is in the liquor, and if present, forms no function iu the digester. This digester is charged with cellulosic material such as spruce chips and an alkaline cooking liquor, which consists of an aqueous solution of caustic soda and sodium sulphide. After the chips have been cooked in the alkaline liquor at the usual temperatures and pressures for the usual lengthv of time, the contents of the digester are delivered through a pipe or conduit 9 to a blow-pit or receptacle 3. Through a screened outlet indicated at 4 a part of the black liquor may be forced by a pump through a pipe. 6 to a tank 7 which for convenience may be termed a tank'for undiluted black liquor. From this tank a certain amount of the black liquor may be cle-- Iivered by a valved pipe 8 to the top of the digester for the next cook, inasmuch as the liquor contains small amounts of sodium sulphide and caustic soda. From the blow-pit 3 the pulp and the remainder of the black liquor` may be forced by a pump 9 through a conduit 10 to any suitable Washing machine, by ,which the pulp is Washed and separated from the black liquor. I preferablylv employ for this purpose a washing machine such as illustrated and described in Letters Patent, No. 1,421,664, dated July 4, 1922, to Brown, Martinson, Moore and Parker. The pulp which is separated during the washing process is transmitted by a conduit 11 to the usual screens (not shown) wherein knots, specks Aand foreign mattei' are rcmoved from the pulp so that the latter may be employed for the manufacture of paper. On the drawing, the washing machine .is only conventionally illustrated and is indicated at 12. Subsequently I will explain the treatment. to which the black liquor is subjected after delivery from the Washing machine 12.

At 13 I have indicated a digester for tlu` digestion of cellulosic material in an acid cooking liquor, and to distinguish it, this digester is here referred to as the sulphite di-v gester, inasmuch as the cooking j. liquor is acid. In this case the cooking liquor consists of an acid solution of a soluble sulphate and preferably a soluble sulphite such as disclosed in my application, Serial No. 661,240,

. filed September 6, 1923, concurrently herewith. Preferably this acid liquor comprises about 4% to 7% free SO2 and about 0.2% to 2%y combined S012 as sodium sulphiteand about 2% to 4% sodium sulphate. In this case it will be noted that the basic metal emdigester are blown through the blow-pipe 14 to a blow-pit indicated at 16.

From this blow-pit the waste liquor and the pulp are forced by a pump 17 through a conduit 18 to a storage tank 19, from which they are pumped by a pump 20 through a conduit 2l to a pulp washing machine indicated as a whole at 22. This washing machine is preferably substantially similar to that indicated conventionally at 12. After the separation of the pulp from the waste liquor, it is conducted -through a conduit 23 to the usual screens (not shown) prior to the formation of the screened pulp intov paper. The pulp produced by the ycooking operation in digester No. 1 is herein termed sulphate pulp, while that produced from the digester 13 is designated sulphite pulp, partly because of the commercial usage of the former term and'in order to distinguish the pulp produced in the digester 13 from that pulp commercially known as sulphate pulp.

There remains now to be described the means by. which the soda is 'recovered from the Waste liquor on the two sides of the system and utilized in both processes of digestion. In each case the waste liquor is concentrated by the evaporation of a portion of its water content in any convenient manner and the residuum is smelted in a smelting furnace for the recovery of the soda in one or another of several compounds. Preferably for the concentration of the waste liquor in each case I employ a multiple-effect evaporator, that for the alkaline waste liquor being indicated conventionally at 24 and that for' the acid liquor being indicated at 25. On the drawing it will be observed that there is a conduit 26 for delivering the alkaline waste liquor to the multiple-effect evaporator 24 and a conduit 27 for delivering the acid liquor from the washing machine to the multiple-effectevaporator 25.l 28 and 29 indicate two smelting furnaces. Preferably I employ that type of combined smelt ing and boiler furnace which is illustrated and described in the' patent to' Moore and Quinn, f No. 1,326,414, dated December 30, 1919, in which case the waste liquor is first heated whileN maintained under external pressure so as to generate therein an eX- plosive force so that when liberated inthe combustion chamber of the furnace the waste liquor is disintegrated and the combustible content thereof consumed, and although on the drawing the ',furnaces are only conventionally indicated, one may, by referring to the Letters'Patent last herein referred to, obtain the details of the furnaces which I prefer to employ. There isthis difference,

however, between the two furnaces which I utilize; namely, that in one case the smelt is subjected to a reduclng atmosphere, where.- as, in the other, the smelt is subjected to an oxidizing atmosphere.

In the present instance the furnace in which a reducing atmosphere is maintained is that indicated at 28, in order that a part of the soda may be recovered as sodium sulphide as well -as sodium carbonate, whereas that at 29 is the one in which the molten vsoda is subjected to an oxidizing atmosphere for -its recovery as sodium sulphate and sodium carbonate. In order to .neutralize the acid waste liquor on the sulphite side of the system, a suflicient quantity of the evaporated alkaline black liquor isdiverted from the conduit 129, leading from the evaporators 24, to the washing machines 22 by means of a pipe 130. The effluent from the furnace 29 is delivered to. a dissolving tank 33 containing water or an alkaline liquor, from which it maybe drawn for acidulation by SO2. This solution which, it will be recalled, contains both. sulphate'and carbonate of` soda, is now ready to be acidulated for use in digester 13 for the production of sulphitc pulp. Anyl suitable apparatus maybe utilized for acidulating this liquor, so that I have indicated conventionally at 45 a pair of towcrs through which lthe alkaline solution may be passed in series and in counter-current flow to SO2 gas for supplying the solution with W suflicient sulphur dioxide to convert thc sodium carbonate to sodium sulphite `and to fur# nish the solution with the requisite amount of free SO2. On the drawing, I have indicated a pump 46 by which the alkaline liquor from the dissolving tank 33 is pumped through a pipe 47 to the top of thc left-hand tower indicated at 45. Each lof these towers is preferably provided with a mass of inert interstitial material such as spiral brick, The liquor after passing through the lefthand tower is pumped by pump 48 through pipe 49 to the top of the right-hand tower,-

and after emerging from the bottom of the last-mentioned tower is delivered by a conduit 50 toa storage tank 51, from which it may be forced by a pump 52 through pipe there is no intention on my part to indicate that other forms of apparatus may not be used, as ordinarily I employ acid gas such as relieved from the sulphite digester in effecting a high acidulation of the liquor.

The smelt from the reducing smelting furnace 28 is delivered into a dissolving tank 44 containing water so that the sodium compounds which are soluble may be dissolved therein. This solution comprising sodium sulphide and sodium carbonate (and some adventitious sodium sulphate) ordinarily requires to be causticized b v the addition of lime and consequently I have illustrated on the drawing at 30 a causticizing tank equipped with an agitator, to which the liquor from the dissolving tank 44 is pumped by pump 315 through pipe 31. A sufficient quantity of lime is added for reaction with the sodium carbonate for the production of caustic soda. After the causticizing operation, the liquor is pumped by a pump 35 through a conduit 36 and a filter press 87 to a mixing tank 38. so that there may now be added to the alkaline liquor sufficient caustic soda to make upsodium losses occurring in the digestion and the recovery of the soda in both the sulphite and the sulphate sides of the system. I have indicated conventionally at 39 a tank for containing a caustic soda solution, a portion of the contents of which may be delivered through a valve pipe 40 to the mixing tank 38. From this mixing tank the alkaline liquor may now be pumped by a pump 41 through a pipe 42 to the sulphate digester 1 for the cooking of a fresh batch r ot' dchips. As there are sulphur losses in the cooking operation. any deficiency in sulphur may be made up by adding sulphur to the mixing tank from a receptacle 43, and/or by adding sulphur to the Vwaste liquor from the digester 13 prior to its delivery to the reducing furnace 28.

From the foregoing description, it will be apparent that the soda which is initially dissolved in the acid liquor employed in the pro- Y duction of the sulphite pulp is recovered and utilized an acid liquor for the production otl sulphite pulp, and, likewise, the soda in the waste alkaline liquor from the sulphate digester is recovered and may be employed in preparing the alkaline liquor for the production of sulphate pulp. But a part or the entire amount of the alkaline waste liquor from the sulphate pulp side of the system is mixed with the acid waste liquor on the sulphite pulp side, to effect the neutralization thereof and also to make up soda losses therein. Consequently, some of the soda in a soluble form is carried in a complete cycle through both digesters.

There are many other advantages incident to the process which I have herein described and which will be apparent to those skilled in the art without my attempting to enumerate them. I may advert to the fact, however,` that there is a decided advantage in employing as raw materials only caustic Soda and sulphur, both of which, (except for such sulphur as is employed in the form of SO2 in acidfying the liquor for the sulphite digestion), as previously stated, may be introduced in the sulphate side of the system herein described. It is true that in practical operation due to the impossibility of maintaining a relative pulp production on both sides of the system, a certain quantity of lime must also be employed for causticizing the soda ash prior to its delivery to the sulphate side of the system, but it is quite apparent that the amount 'of lime which thus must be employed is less than that which is ordinarily employed in the usual sulphate process of pulp production.

`I may call attention to the fact that in the production of sulphite cooking acid in producing the sulphite pulp. sodium carbonate as delivered from the sulphate side' of the system neutralizes the.. waste acid liquor from the sulphite digester prior to its evaporation. In any event, this requires replacement in the sulphate cycle of sodium constituents, preferably in the form of caustic soda. Ordinarily in the production of sulphate pulp. losses in the soda constituent are made up by the addition of sodium sulphate to the smelting furnace employed in the recovery of the soluble inorganic content of the Waste alkaline liquor, and I should not regard it as a departure from my invention if certain sodium losses were made up by adding sodium sulphate to the concentrated waste alkaline liquor prior to its combustion in the combined smelting and boiler furnace 28 for reduction as sulphide, in which case one may also compensate for such sodium carbonate in the waste alkaline liquor for neutralizing the waste acid liquor, by supplying caustic soda to the alkaline cooking liquor; and sulphur losses in the sulphate cycle may be made up by the addition of sulphur to the alkaline cooking liquor. In this case the added sulphate might represent chemical losses in the sulphate cycle,and the added caustic soda represent losses in the sulphite cycle. If the production of pulp onl the sulphite side of thesystem were great enough relatively to that on the sulphate side,.so as to require for the neutralization of the acid waste liquor all the alkaline waste liquor from the sulphate digester, then in such case the flow of concentrated liquor from the evaporators ,24, 24, could be diverted past the furnace4 28, which could be shut down, and, further, all the raw make-up materials," i. e., caustic soda and sulphur (except such sulphur as employedy for acidifying the acid cooking liquor) could be added to plain water supplied to the mixing tank 38 for producing the alkaline cooking liquor, the caustic soda and sulphur being suiiicient in proportion to produce the desired sulphidity and causticity of the liquor. This would be advantageous in dispensin`g with the use of lime for causticizing purposes.

-While .I havedescribed my process as practical in` connection with sulphate pulp and sulphite pulp, it'could be practical making soda pulp and Sulphite pulp, 1n which case the molten sodium compounds in furnace 28 would be subjected to an oxidizing vatmosphere for the production of so dium carbonate. In this case, no sulphur would be added to the caustic alkaline cooking liquor, but would be utilized as SO2 in makingthe acid cooking liquor. Caustic soda would be used as the raw make-up material in forming the alkaline cooking liquor.

On the drawing, which is wholly conventional and diagrammatic, I have made no attempt to indicate the relative dimensions and location of the various instrumentalities or to show the details of the several instrumentalities. For example', I have omitted, as being no part of the present invention,

' any meansfor rec-overin and using the relief from the sulphite digester, or the SO2 from the blowpit vapors and gases, or anyplication Serial No. 661,240.

1. A processv of manufacturing chemical wood pulp, comprising cooking raw cellulosic material in a sulphurous acid solution of sodium sulphate, smelting the inorganic content of the wast-e liquor together with the inorganic content of awaste alkaline cooking liquor and recovering soluble inoiganic compounds in an aqueous solution, acidifying such solution' with sulphur dioxide, and cookin a fresh batch of cellulosic material therewith.

2. A process of manufacturing chemical wood pulp, which comprises cooking raw cellulosic material in a caustic alkaline solution comprising sodium salts, neutralizing waste acid cooking liquor containing sodium compounds with the waste alkaline cooking liquor resulting froml said cooking liquor, concentrating said neutralized liquor, smelting the sodium compounds thereof in an oxidizing atmosphere and recovering the soluble sodium compounds in an aqueous solution, then acidifying such solution with sulphur dioxide, and cooking raw cellulosic material therewith.

- 3. A process such as herein set forth, which comprises concentrating waste alka` line cooking liquor containing caustic soda, smelting the sodium compounds in a reducing atmosphere and recovering the same in an 'aqueous solution, concentrating waste acid cooking liquor containing sodium salts, neutralizing said last-mentioned acid liquor with a portion of the first-mentioned alkaline liquor, smelting the sodium compounds of the' neutralized liquor in an oxidizing atmosphere and recovering the same in an aqueous solution, acidifying said last-mentioned solution with SO2, and cooking raw cellulosic material therewith.

4. A process such as herein set forth,

which comprises concentrating` waste alkaline cooking liquor containing caustic soda andy sodium sulphide,smelting the sodium compounds in a reducing atmosphere .and recovering the same in an aqueous solution, concentrating waste acid cooking-liquor containing sodium salts, neutralizing .said lastvmentioned acid liquor with a portion of the first-mentioned alkalineliquor, smelting the sodium compounds of the neutralized liquor in an oxidizing atmosphere and recovering the same in an aqueous solution, acidifying said last-mentioned solution with SO. and cooking raw cellulosic material therewith.

5. A process such as herein' set forth, which comprises concentrating waste alkaline cooking liquor containing caustic soda, smelting the sodium compounds in areducing atmosphere and recovering the same in an aqueous solution, causticizing said solution with lime andrenioving the insoluble calcium carbonate therefrom, adding soluble sodium compounds thereto so that the same may be employed as an alkaline cooking liquor for raw cellulosic material, concentrating a waste acid cooking liquor containing sodium salts, mixing therewith a neutralizing amount of the iirstsaid waste alkaline cooking liquor, smelting the sodium compounds of said neutralizing liquor in an oxidizing atmosphere and recovering sodium salts in an aqueous solution, and acidifying said last-mentioned solution so that the same may be employed as an acid cooking liquor for raw cellulosic material.

6. A process such as herein set forth, which comprises concentrating Waste alkaline cooking liquor containing caustic soda and sodium sulphide, smelting the sodium compounds in a reducing atmosphere and recovering the same in an aqueous solution, causticizing said solution with lime` and removing the insoluble calcium carbonate therefrom, adding sulphur and soluble sodium compounds thereto so that the same may be employed as an alkaline cooking liquor for raw cellulosic material, concentrating a Waste acid cooking liquor containing sodium salts, mixing therewith a neutralizing amount of the first said Waste alkaline cooking liquor, smelting the sodium compounds of said neutralized liquor in an oxidizing atmosphere and recovering sodium salts in an aqueous solution, .and acidifying said last-mentioned solution so that the same may be employed as an acid cooking liquor for raw cellulosic material.

7. A process such as .herein described, which comprises concentrating Waste acid cooking liquor containing sodium sulphate and sodium sulphite, smelting the inorganic compounds in an oxidizing atmosphere and recovering the same in an aqueous solution, acidifying such solution with sulphur dioxide, cooking raw cellulosic material there- With, and replacing losses of sodium compounds in said operations by mixing with said irstmentioned Waste liquor the alkaline black liquor resulting from the digestion of cellulosic material with a sodiumsulphide caustic-soda cooking liquor.

In testimony whereof I have aflixed my signature.

GEORGE A. RCHTER. 

